Showing papers in "Analytical Communications in 1999"
TL;DR: With a higher sensitivity as a chromogenic indicator for cell viability compared with conventional tetrazolium salts, WST-8 produced results of cell viability and IC50 values that were in good agreement, respectively, with the MTT method and [3H]thymidine uptake method.
Abstract: The application of a tetrazolium salt, 2-(2-methoxy-4-nitrophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H tetrazolium, monosodium salt (WST-8), to cell viability assays and in vitro drug sensitivity tests is described. With a higher sensitivity as a chromogenic indicator for cell viability compared with conventional tetrazolium salts, WST-8 produced results of cell viability and IC50 values that were in good agreement, respectively, with the MTT method and [3H]thymidine uptake method.
569 citations
TL;DR: In this paper, a micromixer for the laminar flow regime based on the principle of flow lamination is presented, which is made up from a glass/silicon/glass sandwich, has a total internal volume of ≡600 nL and measures 5 mm × 10 mm.
Abstract: This paper presents a micromixer for the laminar flow regime based on the principle of flow lamination. The structure is made up from a glass/silicon/glass sandwich, has a total internal volume of ≡600 nL and measures 5 mm × 10 mm. Flow rates between 1–200 µL min–1 have successfully been used. Fluorescence quenching experiments were carried out for quantification and showed 95% mixing within 15 ms.
376 citations
TL;DR: The successful imprinting against model compounds with very different hydrophobicities demonstrates the generality of the current simple approach and yields monodisperse, spherical polymer particles in the micron-scale range, quickly, cleanly and in good yield.
Abstract: In the present study, molecularly imprinted affinity sorbents against theophylline and 17β-estradiol are synthesised via precipitation polymerisation, a synthetic method that yields monodisperse, spherical polymer particles in the micron-scale range, quickly, cleanly and in good yield. The specific binding sites that are created during the imprinting process are analysed via radioligand binding analysis. The molecularly imprinted microspheres are highly specific and have higher load capacities compared to the ‘classical’ particles obtained by grinding the imprinted monolith. The successful imprinting against model compounds with very different hydrophobicities demonstrates the generality of the current simple approach.
293 citations
166 citations
TL;DR: In this article, an enantioselective chemical sensor was designed and fabricated based on a molecularly imprinted polymer, serving as the recognition element, and a quartz crystal microbalance (QCM), used as the transducer.
Abstract: An enantioselective chemical sensor has been designed and fabricated. The sensor is based on a molecularly imprinted polymer, serving as the recognition element, and a quartz crystal microbalance (QCM), used as the transducer. The polymer, imprinted with the chiral β-blocking drug S-propranolol, was cast as a thin permeable film onto a gold electrode deposited on the quartz crystal vibrator. The mass increase of the polymer due to analyte binding was quantified by piezoelectric microgravimetry with the QCM. The sensor was able to discriminate between the R- and S-propranolol enantiomers in acidified acetonitrile solutions owing to the enantioselectivity of the imprinted sites. Detectability of S-propranolol was 50 µmol dm–3. The general procedure developed here for preparation of the sensor can be adapted for fabrication of a range of different stable analytical sensing devices for numerous analytes by using conventional molecular imprinting protocols.
138 citations
TL;DR: In this paper, the principal selenium compounds in these samples were identified as selenomethionine, and Se-adenosyl-selenohomocysteine in yeast, and γ-glutamyl-Se-methyl-SEN-EN in garlic.
Abstract: Selenium-enriched garlic and yeast sample extracts and digests were analyzed using ion-pair high performance liquid chromatography (HPLC) with on-line inductively coupled plasma-mass spectrometric (ICP-MS) and electrospray ionization-mass spectrometric (ESI-MS) detection. The principal selenium compounds in these samples were identified as selenomethionine, and Se-adenosyl-selenohomocysteine in yeast, and γ-glutamyl-Se-methyl-selenocysteine and possibly γ-glutamyl-selenomethionine in garlic. The compounds identified account for 85 and 90% of the total selenium content of the yeast and the garlic samples, respectively. On-line HPLC-ESI-MS selected ion chromatograms (SIC) and mass spectra of selenium compounds extracted from selenium enriched samples are presented. Limits of quantification (LOQ, defined as S/N = 10) for HPLC-ICP-MS were in the range 10–50 ng mL–1 Se in the injected extracts. LOQ values for HPLC-ESI-MS were ca. 100 times higher than those of HPLC-ICP-MS.
107 citations
TL;DR: In this paper, an approach to the identification of unknown signals in selenium speciation analysis of yeast by reversed-phase chromatography with ICP-MS detection is described.
Abstract: An approach to the identification of unknown signals in selenium speciation analysis of yeast by reversed-phase chromatography with ICP-MS detection is described. The analytical strategy was based on: (i), heart-cutting of a Se-containing fraction in the reversed-phase chromatographic eluate followed by its lyophilization; (ii), pneumatically-assisted electrospray (ESI) MS and ESI tandem MS of the lyophilizate; and (iii) confirmation of the fragmentation pattern obtained using the sulfur analogue of the seleno compound that was expected to have been identified. The approach developed allowed the identification of Se–adenosylhomocysteine as the major selenium species in an extract of a selenized yeast sample.
106 citations
TL;DR: In this paper, the use of a solid phase micro-extraction (SPME) method with poly(3-methylthiophene) coated platinum micro-fiber electrodes to extract arsenate ions from aqueous solutions without derivatization is described.
Abstract: The use of a solid phase micro-extraction (SPME) method with poly(3-methylthiophene) coated platinum micro-fiber electrodes to extract arsenate ions from aqueous solutions without derivatization is described. The fibers were fabricated by cycling the working electrode between –0.20 and +1.7 V (vs. Ag/AgCl) in an acetonitrile solution containing 50 mM 3-methylthiophene monomer and 75 mM tetrabutylammonium tetrafluoroborate (TBATFB) electrolyte. All electrochemical procedures (extraction and expulsion) were conducted in a three-electrode system. After fabrication, the conducting polymer film was immersed in the sample solution and converted to its oxidized, positively charged form by applying a constant potential of +1.2 V with respect to Ag/AgCl reference electrode. Arsenate ions migrated into the film to maintain electroneutrality. Upon subsequent reversal of the potential to –0.60 V vs. Ag/AgCl, the polymer film was converted to its reduced, neutral form and the arsenate ions were expelled into a smaller volume (200 µL) of de-ionized water for analysis using flow injection with inductively coupled plasma mass spectrometric (ICP-MS) detection.
82 citations
TL;DR: A molecularly imprinted solid phase extraction-differential pulsed elution (MISPE-DPE) method has been developed for the determination of nicotine in tobacco as mentioned in this paper, which provided inherent selectivity for nicotine that allowed both a shorter analysis time (3 min) and a lower analysis cost than liquid chromatographic methods.
Abstract: A molecularly imprinted solid phase extraction-differential pulsed elution (MISPE-DPE) method has been developed for the determination of nicotine in tobacco. Nicotine and a trace alkaloid myosmine were able to bind to the molecularly imprinted polymer (MIP) packed in a micro-column when acetonitrile was used as the mobile phase. However, over 95% of the bound myosmine could be desorbed and washed away by a 20 µl pulse of methanol, compared to only 43% of the bound nicotine. The remaining quantity of bound nicotine was desorbed by a 20 µl pulse of 1% trifluoroacetic acid in water, for direct UV detection at 254 nm. This MISPE-DPE method provided inherent selectivity for nicotine that allowed both a shorter analysis time (3 min) and a lower analysis cost than liquid chromatographic methods. A detection limit of 1.8 µg ml–1 and a linear dynamic range up to 1000 µg ml–1 were obtained. Preconcentration of 845 µl of a 10 ng ml–1 nicotine standard solution produced a detectable peak signal. These analytical figures of merit are superior to those reported previously for several nicotine–MIP-based methods.
70 citations
TL;DR: In this paper, the polymer obtained from equimolar amounts of methacrylic acid and 4-vinylpyridine was found to recognize bentazone better than other polymers, both in chloroform and acetonitrile.
Abstract: Polymers able to bind the pesticide bentazone were prepared by utilising the technique of the non-covalent molecular imprinting polymerisation and using different molar ratios of methacrylic acid and 4-vinylpyridine as interacting monomers. Polymers obtained were packed in HPLC columns and the imprinting effect was studied using chloroform and acetonitrile as mobile phase. The polymer obtained from equimolar amounts of methacrylic acid and 4-vinylpyridine was found to recognise bentazone better than other polymers, both in chloroform and acetonitrile. The bentazone capacity for this stationary phase was studied considering aqueous buffers with different pH values and ionic strengths. A preliminary procedure of solid phase extraction was tested on aqueous samples containing a fixed amount of bentazone. Good recoveries (91–96%) and concentration factors of 3.2–15.2 were found.
64 citations
TL;DR: In this paper, the influence of temperature in the range 75-180 °C on the solvation properties of pressurized water is studied by use of chromatography for a varied group of compounds on a porous polymer sorbent PLRP-S 100.
Abstract: The influence of temperature in the range 75–180 °C on the solvation properties of pressurized water is studied by use of chromatography for a varied group of compounds on a porous polymer sorbent PLRP-S 100. The solvation parameter model is used as the basis of a quantitative comparison of the influence of temperature and solvent composition variation on the elution strength and selectivity of the mobile phase. The predominant influence of increasing temperature on the solvation properties of water is to reduce its cohesion and capacity for hydrogen-bond interactions. Even at 180 °C, however, hot water retains sufficient of its room temperature properties to remain a relatively weak eluting solvent in reversed-phase chromatography compared with aqueous mixtures of miscible organic solvents. Changes in selectivity accompanying composition variation for acetonitrile, methanol, and propan-2-ol are quantitatively different from those demonstrated for temperature variation of pressurized water, indicating that for method development the two processes are complementary rather than redundant.
TL;DR: In this article, the synthesis of a ruthenium(II) polypyridyl complex incorporating silane pendant moieties is described, which was covalently bound to an organically modified silica glass precursor to give thin films suitable for optical oxygen sensing.
Abstract: The synthesis of a novel ruthenium(II) polypyridyl complex incorporating silane pendant moieties is described. This fluorescent material was covalently bound to an organically modified silica glass precursor to give thin films suitable for optical oxygen sensing. These films showed good oxygen sensitivity characteristics, and possess the distinct advantage over physically entrapped dyes of being chemically attached to the support membrane. This approach to the preparation of luminescent micro-porous glass films provides sensitive membranes suitable for applications where zero dye leaching is a requirement.
TL;DR: In this paper, a capillary electrophoresis-electrochemistry chip constructed from low-temperature co-fired ceramic (LTCC) tape is presented, which is the first report of such a chip constructed in this manner using these materials.
Abstract: A capillary electrophoresis–electrochemistry chip constructed from low-temperature co-fired ceramic (LTCC) tape is presented. This is the first report of such a chip constructed in this manner using these materials. Electroosmotic flow at pH 7 is demonstrated by the migration of a neutral marker, catechol. The separation and detection of two phenolic compounds are presented.
TL;DR: In this paper, the solvation parameter model is used to construct models for estimating the non-specific aquatic toxicity of organic compounds to the fathead minnow, guppy, golden orfe, water flea and the prokaryote Vibrio fischeri.
Abstract: The solvation parameter model is used to construct models for estimating the non-specific aquatic toxicity of organic compounds to the fathead minnow, guppy, golden orfe, water flea and the prokaryote Vibrio fischeri. Size is the characteristic solute property promoting toxicity and solute hydrogen-bond basicity in reducing it. Interspecies differences in toxicity result from differences in the above properties and also because of significant differences in the hydrogen-bond basicity and dipolarity/polarizability of biomembranes. In general, the octanol–water or dimyristoylphosphatidylcholine–water distribution systems are not good surrogate models for the aquatic toxicity for any of the species studied. The retention factor in correlation models for selected chromatographic systems is a suitable descriptor for estimating non-specific aquatic toxicity of organic compounds for some species, such as the tadpole and guppy.
TL;DR: It was confirmed that initial binding of the ERE with ER is significantly accelerated by the formation of an E–ER complex, and the proposed technique is simple, flexible and cheap and has great potential in applications such as field and on-site monitoring and screen testing of endocrine disruptors.
Abstract: A new methodology, sandwich-type monitoring assay system using an estrogen response element (ERE)-immobilized piezoelectric biosensor in combination with flow injection technique, has been developed for analysis of estrogen (E). The principle of the assay is that the estrogen receptor (ER) captures estrogen and then the complex is bound with ERE immobilized on the sensor. It was confirmed that initial binding of the ERE with ER is significantly accelerated by the formation of an E–ER complex. This kinetic difference was monitored by real-time measurement of the resonance frequency of the ERE piezoelectric biosensor and applied to detect 17β-estradiol. The calibration graph was linear in the range 10–100 nmol l–1 with a detection limit of 7.8 nmol l–1, an RSD of 5.9% for 50 nmol l–1 (6 replicates), and one run time of 4 min. Gradient flow injection on-line connection to an array of ERE piezoelectric biosensors is in progress for the simultaneous determination of endogenous and synthetic estrogens in drinking water and urine. In comparison with present chromatographic methods coupled with MS, the proposed technique is simple, flexible and cheap and has great potential in applications such as field and on-site monitoring and screen testing of endocrine disruptors.
TL;DR: The potentiometric biosensor for glucose based on processible polyaniline has been developed using a non-aqueous enzymology approach for enzyme immobilization and was useful for glucose detection over the concentration range 0.1–30 mM and the maximum response value reached was ≈80 mV.
Abstract: Processible polyaniline (PCPAn) modified electrodes are characterized by an advanced potentiometric pH response in comparison to those based on regular polyaniline. Glassy carbon electrodes modified with PCPAn by dip-coating exhibited a fully reversible potentiometric response of approximately 90 mV pH–1 over the range pH 3–9. Such significantly higher potentiometric responses of PCPAn modified electrodes compared to existing devices is explained on the basis of the thermodynamics of polyaniline redox reactions. The potentiometric biosensor for glucose based on processible polyaniline has been developed using a non-aqueous enzymology approach for enzyme immobilization. In the model solution, which mimics blood serum, the biosensor was useful for glucose detection over the concentration range 0.1–30 mM and the maximum response value reached was ≈80 mV. The advanced potentiometric response of PCPAn modified electrodes provides their application for sensor and biosensor development.
TL;DR: In this paper, the ion-selective electrode based on calix[4]arene tetra(propyl ether) was successfully applied to thallium(I) assays in human urine.
Abstract: Calix[4]arene derivatives have been applied as neutral carriers for thallium(I)-selective electrodes, taking advantage of their π-coordination. Calix[4]arene derivatives without any t-butyl group at the upper rim, such as calix[4]arene tetra(propyl ether) and tetra(allyl ether), provided the thallium(I)-selective electrodes with high sensitivity and ion selectivity. t-Butylcalix[4]arene derivatives employed here did not afford very good results as for the thallium(I) neutral carrier. 1H-NMR spectroscopy indicated that thallium(I) complexation by the calixarene neutral carriers is made primarily by π-coordination of their skeletal aromatic rings. The ion-selective electrode based on calix[4]arene tetra(propyl ether) was successfully applied to thallium(I) assays in human urine.
TL;DR: Molecularly imprinted polymers to penicillin V or oxacillin were prepared, and their recognition properties were investigated, both in organic and aqueous phases, indicating that MIPs can be used to prepare either selective or general recognition matrices for penicillins.
Abstract: Molecularly imprinted polymers (MIPs) to penicillin V or oxacillin were prepared, and their recognition properties were investigated, both in organic and aqueous phases. The resulting MIPs proved to be efficient in distinguishing between different penicillins (penicillin V, penicillin G and oxacillin), but could also be prepared to recognise the penicillins as a group. The results indicate that MIPs can be used to prepare either selective or general recognition matrices for penicillins, which can be of potential use in separation and detection applications.
TL;DR: An improved amperometric biosensor based on a solid binding matrix (SBM) composite transducer has been used for the determination of D-fructose in foodstuffs samples as mentioned in this paper.
Abstract: An improved amperometric biosensor based on a solid binding matrix (SBM) composite transducer has been used for the determination of D-fructose in foodstuffs samples. The enzyme, D-fructose dehydrogenase (EC 1.1.99.11), was incorporated directly into a solid composite transducer containing both 2-hexadecanone as SBM and chemically modified graphite. Hexacyanoferrate(III) was used as a redox mediator and the current variation caused by the presence of D-fructose was measured amperometrically. The electrochemical properties and the characteristics of the composite fructose biosensors are described. The amperometric signals were fast, reproducible and linearly proportional to D-fructose concentrations in the range 50 × 10–6–10 × 10–3 mol l–1, with a correlation coefficient of 0.999. A set of measurements at +0.20 V versus SCE for 2 × 10–3 mol l–1D-fructose yielded a relative standard deviation for the steady-state current of 2.11%. The use of a chemically modified graphite by a mild oxidation step was shown to improve the biosensor selectivity against anionic interferents such as L-ascorbate. The biosensor proved to be stable for 6 months and the assay of D-fructose by this electrode was not influenced by the presence of sugars or other interferents commonly found in food samples. The biosensor was used for the determination of D-fructose in some food samples, and the results were consistent with those obtained with the commercially available D-fructose enzyme photometric kit.
TL;DR: This paper presents a simple assay for the estimation of the amount of glucose oxidase immobilised onto the surface of enzyme electrodes, and is verified for a monolayer enzyme electrode using a quartz crystal microbalance.
Abstract: This paper presents a simple assay for the estimation of the amount of glucose oxidase immobilised onto the surface of enzyme electrodes. The two flavin adenine dinucleotide (FAD) cofactors were stripped from immobilised glucose oxidase using an 8 M urea solution. The resultant concentration of FAD in the urea solution was quantified using either fluorescence or voltammetry to determine the amount of glucose oxidase on the electrode surface. The assay is applied to a variety of different enzyme electrodes and is verified for a monolayer enzyme electrode using a quartz crystal microbalance.
TL;DR: A gas chromatographic system has been developed for the direct analysis of atmospheric formaldehyde and other oxygenated hydrocarbons as discussed by the authors, which uses the trapping of analytes in a loop cooled with liquid nitrogen, separation by gas chromatography and then subsequent detection using a pulsed discharge helium ionisation detector (pdHID).
Abstract: A gas chromatographic system has been developed for the direct analysis of atmospheric formaldehyde and other oxygenated hydrocarbons. This method utilises the trapping of analytes in a loop cooled with liquid nitrogen, separation by gas chromatography and then subsequent detection using a pulsed discharge helium ionisation detector (pdHID). The detection limit of this instrument is estimated to be 32 parts per trillion by volume (pptv) for 0.2 l of gas sampled at a flow rate of 30 ml min–1 (S/N at 4:1). A number of other compounds have been monitored simultaneously using this method, including higher molecular weight aldehydes and acetone. Continuous measurement of formaldehyde can be performed with a time resolution of 15 min, with longer analysis times required for inclusion of other species. Calibrations were performed using a permeation tube instrument for both formaldehyde and acetone. A linear response has been observed for formaldehyde sample volumes of 60–200 ml of a 272 ppbv sample (20–68 ng). For acetone a linear response was observed from 175–360 ml of a 30 ppbv standard (12–26 ng). A flame ionisation detector (FID) was also utilised during system development to confirm separation of formaldehyde from atmospheric hydrocarbons.
TL;DR: In this article, mixedmode capillary electrochromatography is introduced as a method for selectivity manipulation in the separation of charged analytes and is investigated for a number of analytes.
Abstract: In this work, mixed-mode capillary electrochromatography is introduced as a method for selectivity manipulation in the separation of charged analytes and is investigated for a number of analytes. This concept involves utilising a component of the eluent to permit the chromatographic and capillary electrophoresis (CE) separation mechanisms to contribute in varying proportions to the separation. This approach was first investigated using a combination of CE with reversed-phase liquid chromatography (RP-LC) for hydrophobic, charged analytes (aliphatic sulfonates), and using the concentration of organic modifier in the eluent to control the contributions of CE and RP-LC. However, the use of reversed-phase columns was found to be problematic for mobile phases with less then 50% organic modifier due to the hydrophobicity of the stationary phase causing the column bed to overheat and dry, and low electroosmotic flow (EOF) values (µ ⩽ 17.8 × 10–9 m2 V–1 s–1) caused additional restrictions. In a second case, ion-exchange stationary phases were used, with the type and concentration of a competing anion in the eluent being used to control the contributions of ion chromatography (IC) and CE to the separation. Nine common inorganic anions were separated using a silica based anion-exchange column and phosphate (pH 7.20) or sulfate (pH 8.2) as eluent with direct UV detection at 214 nm and 17 inorganic and small organic anions were separated using a nitrate eluent (pH 6.80) with indirect UV detection at 214 nm. The separation selectivity was shown to be a combination of IC and CE.
TL;DR: An optical oxygen sensor based on the photoluminescent quenching of palladium tetrakis(4-carboxyphenyl)porphyrin (PdTCPP) self-assembled membrane on an alumina plate has been developed, indicating that this membrane is a highly sensitive device for oxygen concentration.
Abstract: An optical oxygen sensor based on the photoluminescent quenching of palladium tetrakis(4-carboxyphenyl)porphyrin (PdTCPP) self-assembled membrane on an alumina plate has been developed. The luminescence intensity of PdTCPP membrane decreased with increase of oxygen concentration, indicating that this membrane is a highly sensitive device for oxygen concentration. The signal changes of this membrane are large enough to allow quantification of oxygen with good sensitivity (I0/I100 > 3). The response times of the sensor are 36 s on going from argon to oxygen and 148 s from oxygen to argon. This is a photostable sensing membrane that exhibits minimal decrease (ca 5%) in initial intensity after continuous irradiation for 24 h.
TL;DR: In this paper, a membrane that is optically sensitive to pH has been prepared by suspending aminated polystyrene microspheres in a hydrogel, which is used for optical sensing in the visible and near-infrared regions, including wavelengths used for fiber optics telecommunications.
Abstract: A membrane that is optically sensitive to pH has been prepared by suspending aminated polystyrene microspheres in a hydrogel. Light crosslinked poly(vinylbenzyl chloride) microspheres with diameters about 1 µm were prepared by dispersion polymerization and aminated with diethanolamine. These microspheres were suspended in a solution of hydroxyethylmethacrylate, which was then polymerized to form a hydrogel. The resulting membranes are turbid because the refractive index of the microspheres is greater than the refractive index of the hydrogel. Turbidity decreases with increasing wavelength. The turbidity of the membranes is greater in a base than in an acid. In acid, protonation of the amine group causes the polymer microspheres to swell. Swelling affects turbidity, both by increasing microsphere diameter and by reducing the microsphere refractive index so that it is closer to the refractive index of the hydrogel. The latter effect dominates in the membranes described here. A simplified theory to describe this behavior yields values that are consistent with observations. These membranes can be used for optical sensing in the visible and near-infrared regions, including wavelengths used for fiber optics telecommunications. They are expected to have excellent long-term stability. However, the microspheres prepared for this study respond very slowly because they are not sufficiently porous to allow easy analyte access to the interior of the polymer.
TL;DR: In this paper, the authors used sol-gel processes to fabricate amperometric biosensors that are active for hypoxanthine (Hx) determination, where Xanthine oxidase was immobilized in the bulk of the silica-graphite matrix (SGM) to produce electrodes where new surfaces can be generated on demand by mechanical polishing.
Abstract: Sol–gel processes were used to fabricate amperometric biosensors that are active for hypoxanthine (Hx) determination. Xanthine oxidase was immobilized in the bulk of the silica–graphite matrix (SGM) to produce electrodes where new surfaces can be generated on demand by mechanical polishing. The immobilized enzyme electrodes can be used in unmediated hydrogen peroxide oxidation mode, or in unmediated and mediated oxygen reduction mode, to result in three different types of Hx biosensors with detection limits of 1.3 × 10–6, 5.6 × 10–6 and 3.8 × 10–7M, respectively. Benzyl viologen was used as the charge transfer mediator to enhance the response in the hydrogen peroxide production mode. The sensors show good linear response over a wide range of concentrations of about 1 × 10–6–1 × 10–3M. The use of bulk immobilization and the possibility of renewable surfaces have enabled the easy operation of these sensors with high stability. The experimental results from a carp sample stored under different conditions demonstrate the practicality of these sensors as simple, rapid and cost effective measurement of fish meat freshness.
TL;DR: In this paper, a Perkin-Elmer SIMAA 6000 simultaneous multielement spectrometer was used to study the correlation between two integrated absorbance signals and an internal standard.
Abstract: Significantly improved performance in electrothermal atomic absorption spectrometry is possible using an internal standardisation technique. A Perkin-Elmer SIMAA 6000 simultaneous multielement spectrometer was used to study the correlation between two integrated absorbance signals. The behaviour of Pb (analyte) in different urine, blood and placenta samples was compared to that of Bi or Tl used as the internal standards. All samples were spiked with known amounts of Pb and Bi or Tl. A satisfactory signal correlation (r = 0.94) between the integrated absorbances for spikes of the analyte and internal standard was observed with Bi as the internal standard. After signal correction, the relative standard deviation of the integrated absorbance for Pb spikes reduced from 29 to 7% for urine, from 19 to 2% for blood and from 22 to 4% for placenta. The mean difference between Pb concentration found in analysed samples by the method of additions and using an internal standard was 10%.
TL;DR: In this article, a two-tube oscillating capillary nebulizer (OCN) was used to test the fritted capillary for possible application to CE-ICP-MS, standard ultraviolet (UV) absorbance detection was used for the CE separation of metallothionein and ferritin.
Abstract: A major experimental consideration, and often a difficulty when interfacing capillary electrophoresis (CE) with plasma mass spectrometry via a pneumatic nebulizer, is the suction effect caused by the natural aspiration of the nebulizer. This has a marked affect on the CE experiment, since it may lead to peak overlap and, ultimately, a completely degraded separation. Placing a sol–gel frit in the sample introduction end of the capillary in a CE system, interfaced with a pneumatic nebulizer at the outlet end of the capillary, minimizes the suction effect. A two-tube oscillating capillary nebulizer (OCN) was used in this study because of its very low liquid flow capacity and potential for interfacing to ICP-MS. To test the fritted capillary for possible application to CE-ICP-MS, standard ultraviolet (UV) absorbance detection was used for the CE separation of metallothionein and ferritin with a grounded nebulizer interface at one end of the capillary. With the capillary frit and OCN interface, reasonably true electropherograms were obtained when compared to the CE separation performed in the traditional mode without a frit and with a buffer reservoir in place at the outlet. Also, during this study it was found that a make-up buffer was necessary to maintain electrical contact to the outlet of the fritted electrophoretic capillary when using the OCN.
TL;DR: A new, fast and sensitive fluorescent probe for the determination of proteins was developed and gave values close to that of the conventional Coomassie Brilliant Blue (CBB) method, but the sensitivity of the method is much superior to the CBB method.
Abstract: A nonfluorescent dimer of Acridine Orange is formed in situ in the presence of the anionic surfactant, sodium dodecyl sulfate (SDS). Proteins labeled with Acridine Orange dimer (AOAO) show a greatly enhanced fluorometric activity compared with that of AOAO. Based on this, a new, fast and sensitive fluorescent probe for the determination of proteins was developed. The linear range of this assay is 0.66–39.8 µg mL–1. For the detection of proteins in human serum, this method gave values close to that of the conventional Coomassie Brilliant Blue (CBB) method, but the sensitivity of the method is much superior to that of the CBB method. The detection limit for BSA was 0.08 µg mL–1.
TL;DR: In this paper, an electrochemical method for the direct detection of aluminium using single-use sensors is described, which consists of three electrodes (working, auxilliary and pseudo-reference) screen-printed with carbon ink.
Abstract: An electrochemical method for the direct detection of aluminium using single-use sensors is described. The sensor consists of three electrodes (working, auxilliary and pseudo-reference) screen-printed with carbon ink. Aluminium is accumulated at the carbon electrode at –1.6 V (vs. pseudo-reference) in zinc sulfate electrolyte for 90 s prior to anodic stripping using differential-pulse voltammetry. Linear calibrations were obtained between 10 and 450 ppb using the aluminium oxidation peak. The limit of detection was 8 ppb Al3+.
TL;DR: In this article, a simple and robust method for the determination of the clinically significant molecule vanilmandelic acid (α,4-dihydroxy-3-methoxybenzeneacetic acid, 4-hydroxy- 3-mETHoxymandelic acid) using flow injection analysis with chemiluminescence detection is described.
Abstract: A simple and robust method for the determination of the clinically significant molecule vanilmandelic acid (α,4-dihydroxy-3-methoxybenzeneacetic acid, 4-hydroxy-3-methoxymandelic acid) using flow injection analysis with chemiluminescence detection is described. This compound was found to enhance the chemiluminescence from the reaction of luminol with hexacyanoferrate(III) in a basic medium. The calibration function obtained over the range from 2.5 × 10–8 to 1.0 × 10–6 mol dm–3 approximated to linearity (r2 = 0.9995) with the equation of best fit of y = 1.72 × 108x + 36.9, where y is the integrated signal (V s) and x is the concentration (mol dm–3). Precision (as measured by relative standard deviation) was 2.6% for 5 replicate analyses of a standard (2.5 × 10–7 mol dm–3) and the limit of detection (3σ) was 2 × 10–8 mol dm–3. Preliminary investigations revealed that the structurally similar homovanillic acid inhibits the emission of chemiluminescence from the luminol–hexacyanoferrate(III) reaction and that the kinetics of light emission were different from those of the vanilmandelic acid enhanced reaction.